Method of handling and replacing pouring tubes of a continuous casting apparatus

ABSTRACT

A method of handling and replacing pouring tubes used for pouring molten metal from a supply vessel into a mold of a continuous casting machine wherein a pouring tube is positioned beneath and in alignment with an outlet of the supply vessel and beneath the surface of a pool of metal in the mold for the purpose of conducting molten metal from the supply vessel into the mold. A replacement pouring tube is positioned at a location removed from the outlet of the vessel and in a position preparatory for exchange of the aforementioned pouring tube located in casting position beneath the outlet of the vessel. Upon the need to replace the pouring tube located in casting position beneath the outlet of the vessel the pouring tubes are displaced along a path such that as the pouring tubes are moved the pouring tube which is beneath the outlet of the vessel is moved out of alignment with said outlet and the replacement pouring tube is moved into alignment with such outlet.

United States Patent Simons et al.

METHOD OF HANDLING AND REPLACING POURING TUBES OF A CONTINUOUS CASTINGAPPARATUS Inventors: Willi Simons, Dusseldorf; Horst Grothe, Kaarst;Rolf Haselhuhn, Dusseldorf, all of Germany; Peter Koenig, Zumikon,Switzerland; Klaus Brock, Dusseldorf, Germany Assignees:Schloemann-siemag Aktiengesellschaft, Dusseldorf, Germany; Concast AG,Zurich, Switzerland; part interest to each Notice: The portion of theterm of this patent subsequent to July 3, 1990, has been disclaimed.

Filed: Apr. 23, 1973 Appl. No.: 353,308

Related US. Application Data Division of Ser. No. 82,750, Oct. 21, 1970,Pat. No. 3,743,007.

Foreign Application Priority Data Oct. 30, 1969 Switzerland 016169/69Nov. 13, 1969 Germany 1957037 US. Cl. 164/82 Int. Cl. B22D 11/10 Fieldof Search 222/533, 537, 545, 548, 222/550, 555, 559, 560, 566,567;164/82, 136, 281, 337

[56] References Cited UNITED STATES PATENTS 3,430,644 3/1969 Lyman137/32906 3,499,587 3/1970 Brock 3,743,007 7/1973 Simons et al. 164/281Primary ExaminerFrancis S. Husar Assistant Examiner.lohn E. RoethelAttorney, Agent, or Firm-Werner W. Kleeman [57] ABSTRACT A method ofhandling and replacing pouring tubes used for pouring molten metal froma supply vessel into a mold of a continuous casting machine wherein apouring tube is positioned beneath and in alignment with an outlet ofthe supply vessel and beneath the surface of a pool of metal in the moldfor the purpose of conducting molten metal from the supply vessel intothe mold. A replacement pouring tube is positioned at a location removedfrom the outlet of the vessel and in a position preparatory for exchangeof the aforementioned pouring tube located in casting position beneaththe outlet of the vessel. Upon the need to replace the pouring tubelocated in casting position beneath the outlet of the vessel the pouringtubes are displaced along a path such that as the pouring tubes aremoved the pouring tube which is beneath the outlet of the vessel ismoved out of alignment with said outlet and the replacement pouring tubeis moved into alignment with such outlet.

9 Claims, 6 Drawing Figures METHOD OF HANDLING AND REPLACING POURINGTUBES OF A CONTINUOUS CASTING APPARATUS CROSS-REFERENCE TO RELATED CASEThis is a divisional of our commonly assigned, copending US.application, Ser. No. 82,750, filed Oct. 21, 1970, now U.S. Pat. No.3,743,007, and entitled Continuous Casting Apparatus withInter-Changeable Pouring Tubes.

BACKGROUND OF THE INVENTION The present invention broadly relates to thecontinuous casting art, and in its more specific aspects concerns a newand improved method of handling and replacing pouring tubes used forpouring molten metal from a supply vessel into a mold of a continuouscasting machine or apparatus without interrupting the continu ouscasting operation.

When operating such continuous casting machines, it is known to feedmolten metal into a tundish from which location the molten metal thenflows into the mold cavity of the continuous casting mold-The metal issupplied to the tundish from a ladle. In the continuous casting ofsteel, the molten metal may be poured into the mold by submerging thelower end of the pouring tube into the molten metal bath within thecontinuous casting mold. This procedure has been found to be veryadvantageous, particularly in reducing oxidation of the molten steel.

With the trend towards increasing weights per heat, and with theintroduction of sequential casting, casting times have beensubstantially prolonged with consequently greater wear on the pouringtubes. As a result, signs of erosive destruction at the pouring tubewithin the bore and in the region of the outlet, are found afterrelatively short casting times. This is especially prevalent whenmanganese-alloy steel is cast. Additional erosion is found when theimmersible pouring tubes penetrate through the surface of the moltenmetal in the mold and when the surface is covered with a layer ofcasting powder in the regions of contact of the pouring tube with thesurface of the molten metal.

It is hardly necessary to emphasize the disadvantageous nature of sucherosion effects. Frequently, the

pouring tubes will break at the thus-weakened regions with resultantentrainment of contaminants into the liquid core of the cast strand andoxidation of the steel. Furthermore, the flow pattern of the moltenmetal becomes changed when such breaks occur irrespective of whetherthey are partial or total and this leads to the conveyance ofcontaminants into deeper regions of the liquid core.

Desirably, therefore, it should be possible to replace weakened orfractured pouring tubes in a simple and rapid manner, in order to avoidthe problems which result from such fracture while at the same timeavoiding expensive downtime of the casting apparatus to the maximumextent possible.

SUMMARY OF THE INVENTION It is, accordingly, an object of the inventionto overcome the above disadvantages and to provide the desirableadvantages which have been outlined.

More particularly, it is an object of the invention to provide animproved method of handling and replacing pouring tubes in continuouscasting apparatus of the type under discussion which affords theseadvantages for the continuous casting apparatus while not beingpossessed of the listed disadvantages.

Another object of the present invention is to provide a method ofhandling and replacing pouring tubes used for pouring molten metal froma supply vessel into a mold of a continuous casting machine in a mannerpermitting replacement of a weakened or defective pouring tube withanother pouring tube, without requiring any shutdown of the castingapparatus so that for all practical purposes the continuous castingoperation proceeds without interruption.

Yet a further object of the present invention is to provide a method ofhandling and :replacing pouring tubes of continuous casting apparatus ina manner wherein it is not only possible to exchange the pouring tubesin an extremely efficient and reliable manner, but simultaneouslycomponents of the flow-regulating device controlling the flow of moltenmetal out of a supply vessel into the continuous casting mold.

Now in order to implement these and still further ob jects of theinvention, which will become more readily apparent as the descriptionproceeds, the method aspects of this development for handling andreplacing pouring tubes used for pouring molten metal from a supplyvessel into a mold at a continuous casting machine contemplatespositioning a pouring tube beneath and in alignment with an outlet ofthe supply vessel and beneath the surface of a pool of metal in the moldfor conducting molten metal from the supply vessel into the mold. Areplacement pouring tube is positioned at a location removed from theoutlet of the vessel and in a position preparatory for exchange of thepouring tube located in casting position beneath the outlet of thevessel. Upon the need to replace the pouring tube located in castedposition beneath the outlet of the was sel, the pouring tubes aredisplaced along a path such that as the pouring tubes are moved, thepouring tube which is beneath the outlet of thevessel is moved out ofalignment with said outlet and the replacement pouring tube is movedinto alignment with such outlet.

According to the invention, the pouring tubes are moved substantially inunison along the aforementioned path. Since the pouring tube which isbeneath the outlet of the supply vessel can be moved out of alignmentwith such outlet and the replacement pouring tube moved into alignmentwith such outlet, it will be appreciated that accordingly one pouringtube can be exchanged for another without interrupting the actualcasting operation. It is, in fact, possible to automate the exchangeoperation and the individual steps involved may be made to overlap intime, so as to further shorten the period required for completing theexchange, necessitating an interruption of metal flow into the mold forless than 30 seconds, and thus making it possible to carry out normallythe exchange without having to interrupt the continuous casting process.

Connecting and disconnecting of the pouring tubes and the outlet of thesupply vessel, typically a tundish, can be facilitated by making boththe pouring tubes and the tundish movable relative to one another,particularly in the direction of metal outflow. To prevent theoccurrence of leaks between the: pouring tube and tundish, and to assurereliable sealing engagement of one with the other, independently ofpossible tolerances in their relative movements, resilient means,typically spring means, may press the relevant pouring tube towards theoutlet of the tundish.

It is desirable that the pouring tube being removed (as defective,weakened, etc.) be withdrawn quickly to make room for its replacement.To facilitate this, the pouring tube may be mounted in or on a guidetrack which advantageously rises from the level of the tundish outlet.It is particularly advantageous to connect the track with the tundish.

When slabs are cast in the apparatus, and when therefore the slab moldhas a correspondingly largedimensioned width, the pouring tubes may beguided in a path for movement into and out of the mold inlet with theirrespective lower portions which is arcuately curved in an upright plane.It is then advantageous to connect the correspondingly curved guidetrack provided for this purpose, with the stationary steel structure andto mount the tundish so that it can be raised and lowered with referenceto the mold.

According to a further aspect of the invention, there can be providedmeans for regulatingvthe outflowof the molten metal through the outletof the tundish. In conventional manner, this can be accomplished byvarying the unobstructed cross-sectional area of the outlet.

However, according to the invention, this means is not necessarilyprovided on the tundish, but instead may be displaceable as a unit withthe pouring tube relative to the outlet. In this manner all componentsof the apparatus which are subject to weakening or damage under theafore-described conditions, can be readily replaced tothus furtherincrease the number of sequential casts obtainable with the tundish.

The path in which the pouring tubes move to and from the operatingposition in which they communicate or are in alignment with the outletof the supply vessel,, may be determined by providing a mounting meanswith arms which are turnable about an upright usually vertical axis andwhich each carries a holding arrangement for holding one of the pouringtubes. It is especially advantageous to mount the arms on a pin or shaftwhich is journalled on the supply vessel itself, for example thetundish, and also can be adjusted to raise and lower the arms withreference to the outlet. The holding arrangements themselves may,however, be turnable with reference to the respective arms and may bearrestable against turning when the longitudinal axis of a pouring tubewhich they hold has a horizontal or substantially horizontalorientation. This makes it possible to keep the vertical displacement ofthe supply vessel or tundish within very small limits, or even to avoidit entirely.

If a pouring tube is moved into operating position in cold state, withthe term here being used in its relative sense as is obvious when oneconsiders that the apparatus operates with molten metal, deleteriousthermal stresses may occur in the fire and heat-resistant material ofthe pouring tubes. Also, the molten metal, such as steel, may solidifyand block their interior passage, especially when the inner diameter issmall. To avoid this, the invention also contemplates the provision ofpre-heating means for pre-heating the pouring tube which is in standbyposition, in other words, a replacement pouring tube which is locatedremoved fromthe outlet of the supply vessel or tundish prior to placingsuch into casting position beneath such outlet.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be betterunderstood and objects other than those set forth above, will becomeapparent when consideration'is given to the following detaileddescription thereof. Such description makes reference to the annexeddrawings showing various exemplary embodiments of apparatus useful forthe practice of the method aspects of this development and wherein:

FIG. 1 is a view in vertical section through one embodiment of apparatusdesigned according to the invention for practicing the inventive method;

FIG. 2 is a similar view, but through another embodiment of theinvention;

FIG. 3 is a section taken on line lII-llI of FIG. 2; FIG. 4 isa viewsimilar to that of FIG. 1, but of yet an additional embodiment;

FIG. 5 is a section taken on line IV-IV of FIG. 4; and

FIG. 6 is a section taken on line VIVI of FIG. 5.

DETAILEDDES CRIPTION OF THE PREFERRED EMBODIMENTS Discussing firstly theembodiment of FIG. I, it will be seen that reference numeral 1identifies a supply vessel, such as typically a tundish, which can beraised and lowered as indicated by the double-headed arrow. The tundish1 possesses an outlet 2 which is provided with a flow-regulating device,here shown as a slide valve 3, by means of which the flow of moltenmetal, such as steel, shown within tundish l but not particularlyidentified with a reference numeral can be varied and stopped asdesired. A pouring tube 5, which may also be called an immersiblepouring tube or casting nozzle, is in operative position in which itconducts the steel from the outlet 2 of tundish 1 into the illustratedcontinuous casting mold 4 tea point below the surface of the moltensteel within such mold. In addition, the pouring tube protects the steelagainst oxidation during travel from the tundish l to the mold 4, andthe lateral outlets or outlet passages 6 which are immersed below thelevel of metal in the mold and through which metal can flow out, providefor improved flow patterns in the liquid core.

It can be seen from the drawing that the outlets 6 of pouring tube 5 arelocated below the surface of the molten steel. In this manner, moltensteel can be conveyed into the mold 4-without being affected orcontaminated by the ambient air. 50 A holding element 7 is turnableabout the pivot axis or shaft 8 and holds the. pouring tube 5 which isretained, as shown, by a conically tapering inner surface 9 of theholding or holder element 7 which prevents it from downward movement,and by outwardly pivotable retaining arms 10 which prevent it fromupward movement.

A resilient means, for instance spring 11, urges or biases the pouringtube holding element 7 with the retained pouring tube 5 towards theoutlet 2 of the supply vessel or tundish l, pressing this pouring tube 5thereagainst when the holding element 7 and the pouring tube 5 are inthe illustrated operative position where the pouring tube Scommunicateswith the inlet of the continuous casting mold 4 below the surface of themetal. The spring 11 assures proper sealing between pouringtube 5 andoutlet 2 even during play in the lifting or descending movement of thetundish 1. Such movement, incidentally, can be accomplished with anyknown means suitable for the purpose and known to those skilled in theart.

In addition to the pouring tube 5, there is provided another pouringtube, identified with numeral 5. This other pouring tube 5 is to berapidly substituted at such time as weakening of pouring tube 5 makesthis desirable, or when fracture of pouring tube 5 makes this stepimperative.

For this purpose, the replacement pouring tube 5 is retained in a holderor holding element 7 which is turnablc or rotatable about a pivot axisor shaft 8; it is shown in FIG. 1 in its standby position. The holdingelements 7 and 7, and therefore the pouring tubes 5 and 5, are connectedby conveyor chain means 12 having runs provided with rollers 13 andlocated at opposite lateral sides of the elements 7 and 7. A guidearrangement or guide means 14 is provided which defines a path in whicheach chain 12 can travel. As the drawing shows, the path rises upwardlyfrom a level below the outlet 2 of tundish 1.

Reference numeral 15 identifies a portion of a frame or otherwisestationary component of the apparatus, and the guide arrangment 14composed of two substantially U-profiled elements of the type shown ismade fast with component 15 at opposite lateral sides of tundish 1. Itis emphasized that such rigid connection is possible only when the inletof the mold is wide so that the lower end of the pouring tube can moveinto and out of the mold 4 see the broken line arrow without requiringlifting of the guide arrangement 14. Of course, no problem exists if thelower end of the pouring tube does not actually extend into the liquidcore.

When the pouring tube 5 is to be replaced with the replacement pouringtube 5, the slide valve 3 is first operated to cut-off the flow ofmetal. The tundish 1 is raised to separate the outlet 2 from the pouringtube 5 and a non-illustrated conventional drive of suitable type, forexample mechanical or hydraulic, is operated to advance the chainstructure and to thereby displace the pouring tubes 5 and 5 in unison inthe curved path defined by guide arrangement 14, as indicated by arrow16. As a result of this, pouring tube 5 moves out of operating positionwhile pouring tube 5 moves into operative position and can be placedinto alignment or flow communication with the outlet 2 of the tundish 1.This takes place during and without interruption of the casting process,i.e. while there is still liquid molten steel moving through the mold 4.Thereupon the tundish l is lowered until outlet 2 sealingly engagespouring tube 5', and the outlet is reopened via slide 3. The defectivepouring tube is removed from its holding element 7 and replaced with anew one, so that the replacement action can be repeated when pouringtube 5 requires substitution except that the movement will then be inopposite direction from the direction shown by arrow 16.

In the embodiment of FIGS. 2 and 3, a supply vessel, namely tundish 21,is connected with an arcuate guide track or track arrangement 22 viacylinder and piston units 23. This permits raising and lowering of trackar' rangement 22 relative to tundish 21 in the direction of outflow ofthe molten metal. In operative position, the pouring tube 5 is againpressed against outlet 2, but here by the units 23. The tundish 21itself may be raised and lowered to permit insertion and removal of thelower end of pouring tube 5 inthe mold 28. Means for raising andlowering of tundish 21 may be of any known type and are therefore notshown.

Here also a replacement pouring tube 5' is provided for standbypurposes. A carriage 29 is movable on rolls 32 in guide trackarrangement 22 and is provided with cylinder and piston units 26 whichhold the pouring tube 5' in place.

In addition, there is provided a preheating device 24 which is movablein the direction of arrow 27 and which is also only shown indiagrammatic form inasmuch as such is well known to those active in thisfield and having routine knowledge. The preheating device 24 isassociated with and serves for heating of the re placement pouring tube5. Of course, if more than one standby pouring tube is provided, morethan one preheating device 24 may also be provided, if desired. Itspurpose has been discussed earlier, and the device 24 is primarilyuseful when the pouring tubes are thick walled and consist, for example,of clay graphite. In this manner, the standby or replacement pouringtube, in this case the pouring tube 5', can be preheated to a desireduniform temperature before it is mounted on carriage 29, or and incertain circumstances this may be advantageous the heating can takeplace while the pouring tube 5 is already connected with the carriage29.

In this embodiment, exchange of pouring tube 5' for pouring tube 5 isinitiated by closing outlet 2 via a stopper or plug 38 which may bemanipulated in known manner from outside the tundish 21. Now the units23 are operated to lower track arrangement 22 in order to separatepouring tube 5 from outlet 2, while at the same time the tundish 21 israised (together with the track arrangement 22) in order to lift thelower end of pouring tube 5 from the mold 28.

Once this is done, the carriage 29 is advanced in the direction of arrow30 through by suitable nonillustrated mechanical, hydraulic or othermeans. The units 23 now lift the track arrangement to sealingly presspouring tube 5' against outlet 2, and it is parenthetically pointed outthat suitable dimensioning of the units 23 makes it possible topre-select this pressure so that the units 23 can additionally act ashydraulic springs. Now the tundish 21 together with track 22 is lowereduntil pouring tube 5' is immersed in the liquid core of mold 28 to thedesire-d depth below the surface of the molten steel, whereupon plug 38is removed and metal flows again to the mold. Of course, if the inlet iswide, or if the pouring tube does not extend into the metal bath,raising and lowering of the tundish 21 and of the track arrangement 22is not necessary, although the movement in track arrangement 22 alone isstill needed.

Details of the track arrangement 22 are shown in the sectional view ofFIG. 3 where it will be seen that two stationary track ring portions 31are each provided with four rollers or wheels 32. which serve to retainand guide carriage 29 in guides 33. The carriage 29 is composed of twoangle-profiled rings 34, connected by ribs 35 which not only serve toprovide carriage 29 with the requisite strength and stability, but alsosupport the units 26 for the pouring tubes 5, 5'.

Coming, finally, to the embodiment of FIGS. 4-6, it will be seen thathere the pouring tubes 5 and 5' can be displaced in unison withrespective flow-regulating devicesfor the outlet 63 of a supply vessel,for instance the tundish6l. i I Reference numeral 64 identifies a guidewhich supports pouring tube inoperative position, together with anapertured sliding plate 65. A similar plate 65 and the standby orreplacement pouring tube 5 are in standby position, held in a guide 64which is pivotably connected with guide 64 as shown.

1 As FIGS. 5 and 6 show, pouring tube 5 is mounted in a plate 72 whichis pivotable on guides 73 about a pivot shaft or axis 74, with referenceto plate 65. The pur pose of this arrangement, in which movement ofplate 72 can be caused, for instance, by means of a laterally mountedcylinder and piston unit 76 which can be coupled to a transmission lever75, is to permit regulating the flow of steel through the outlet 63.

When the unit consisting of plate '65 and pouring tube 5 is to bereplaced, then plate 72 is pivoted to close the outlet 63. Now thetundish 61 is raised and the guides 64' and 64 are swung downwardlyabout the pivot axes or shafts 68 so that they move'to positions inwhich they are horizontally aligned with the guide 64. A cylinder andpiston unit 66 pushes the pouring tube '5 and plate 65 from the guide 64into the guide 64, and simultaneously displaces pouring tube 5 and plate65'from guide 64 into guide 64". Thereafter, the guides 64 and 64 areswung upwardly to the position shown in FIG. 4 (with the new position ofpouring tube 5 shown in broken or phantom lines) and the flow of metalthrough the outlet 63 is restored.

Of course, it should be understood that individual features of one ofthe embodiments could be provided for other embodiments to the extentthat the same are compatible. Thus, for instance, the preheating meansfor heating the replacement pouring tube, as indicated in the embodimentof FIG. 2, could also be provided for any of the other embodiments. Withthe teachings of the invention, it will be recognized that the pouringtube which'is beneath the outlet of the vessel, and for instance whichmust be replaced because it is damaged or otherwise defective, can bemoved out of alignment with the outlet of the supply vessel and thereplacement pouring tube can be moved into alignment with such outlet,without the need to interrupt the continuous casting operation.Furthermore, the damaged pouring tube can then be replaced for a new oneduring such time as=the casting operation proceeds and therefore thesystem is again ready to quickly carry out a new replacement operationfor the pouring tube located in casting position beneath the outlet ofthe supply vessel when the need arises.

While there is shown and described presentpreferred embodiments of theinvention, it is to be distinctly understood that the invention is notlimited thereto, but may be otherwise variously embodied and practicedwithin the scope of the following claims.

Accordingly, What is claimed is: V

l. A method of handling and replacing pouring tubes used for pouringmolten metal from a supply vessel into a mold of a continuous castingmachine without interrupting the continuous casting operation,comprising the steps of positioning a pouring tube beneath and inalignment with an outlet of the supply vessel and beneath the surfaceofa pool of metal in the mold for conducting molten metal from thesupplyvessel into the replace the pouring tube located in casting positionbeneath the outlet of the supply vessel, displacing the pouring tubesalong a path suchthat as the pouring tubes are moved, the pouring tubewhich isbeneath the outlet of the supply vessel is moved out ofalignment with said outlet and the replacement pouring tube is movedinto alignment with such outlet.

2. The method as defined in claim 1, further including the step ofmoving such pouring tubes substantially in unison along said path.

3. The method as defined in claim 1, further includ ing the step oflifting the supply vessel from a casting position relative to the moldimmediately prior to moving the pouring tube which is in its castingposition out of alignment with the outlet of the supply vessel, andimmediately after the replacement pouring tube has been brought intoalignment with the outlet of the supply vessel again lowering the supplyvessel back into its casting position. I

4. The method as placement of the pouring tubes is carried out in unisonwith respective flow-regulating devices for the outlet of the supplyvessel. v

5. The method as defined in claim 1, further including the step ofbriefly initially interrupting the flow of molten metal from the vesselinto themold prior to displacement of the pouring tubes.

6. The method as defined in claim 1, further including the step ofreplacing the pouring tube which has been moved out of alignment withthe outlet of the supply vessel by a new pouring tube after such time asthe other pouring tube has moved into a position beneath the outlet ofthe supply vessel.

7. The method as defined in claim 1, further including the step ofpreheating the pouring tube which is located removed from the outlet ofthe supply vessel prior to placing such into casting position beneaththe outlet of the supply vessel.

8. The method as defined in claim 1, further including the step ofresiliently biasing the pouring tube which is beneath the outlet of thesupply vessel in the direction of such outlet.

9. The method as defined in claim 1, further including the steps whereinupon said need to replace the pouring tube located in casting positionbeneath the outlet of the supply vessel, during a first step closing theoutlet of the supply vessel, then during a second step carrying out saiddisplacing of the pouring tubes along a path such that as the'pouringtubes are moved, the pouring tube which is beneath the outlet of thesupply vessel is moved out of alignment with said outlet and thercplacement'pouring tube is moved into alignment with said outlet, thenduring a third step again opening the outlet of the supply vessel, andduring a fourth step carrying out the aforesaid replacing'of the pouringtube which has been moved out of alignment with the outlet of the supplyvessel by a' new pouring tube after such time as the replacement pouringtube has moved into I a position beneath the outlet of the supplyvessel.

defined inclaim 1, wherein dis-

1. A method of handling and replacing pouring tubes used for pouringmolten metal from a supply vessel into a mold of a continuous castingmachine without interrupting the continuous casting operation,comprising the steps of positioning a pouring tube beneath and inalignment with an outlet of the supply vessel and beneath the surface ofa pool of metal in the mold for conducting molten metal from the supplyvessel into the mold, positioning a replacement pouring tube at alocation removed from the outlet of the supply vessel and in a positionpreparatory for exchange of the first-mentioned pouring tube located incasting position beneath the outlet of the supply vessel, and upon needto replace the pouring tube located in casting position beneath theoutlet of the supply vessel, displacing the pouring tubes along a pathsuch that as the pouring tubes are moved, the pouring tube which isbeneath the outlet of the supply vessel is moved out of alignment withsaid outlet and the replacement pouring tube is moved into alignmentwith such outlet.
 2. The method as defined in claim 1, further includingthe step of moving such pouring tubes substantially in unison along saidpath.
 3. The method as defined in claim 1, further including the step oflifting the supply vessel from a casting position relative to the moldimmediately prior to moving the pouring tube which is in its castingposition out of alignment with the outlet of the supply vessel, andimmediately after the replacement pouring tube has been brought intoalignment with the outlet of the supply vessel again lowering the supplyvessel back into its casting position.
 4. The method as defined in claim1, wherein displacement of the pouring tubes is carried out in unisonwith respective flow-regulating devices for the outlet of the supplyvessel.
 5. The method as defined in claim 1, further including the stepof briefly initially interrupting the flow of molten metal from thevessel into the mold prior to displacement of the pouring tubes.
 6. Themethod as defined in claim 1, further including the step of replacingthe pouring tube which has been moved out of alignment with the outletof the supply vessel by a new pouring tube after such time as the otherpouring tube has moved into a position beneath the outlet of the supplyvessel.
 7. The method as defined in claim 1, further including the stepof preheating the pouring tube which is located removed from the outletof the supply vessel prior to placing such into casting position beneaththe outlet of the supply vessel.
 8. The method as defined in claim 1,further including the step of resiliently biasing the pouring tube whichis beneath the outlet of the supply vessel in the direction of suchoutlet.
 9. The method as defined in claim 1, further including the stepswherein upon said need to replace the pouring tube locAted in castingposition beneath the outlet of the supply vessel, during a first stepclosing the outlet of the supply vessel, then during a second stepcarrying out said displacing of the pouring tubes along a path such thatas the pouring tubes are moved, the pouring tube which is beneath theoutlet of the supply vessel is moved out of alignment with said outletand the replacement pouring tube is moved into alignment with saidoutlet, then during a third step again opening the outlet of the supplyvessel, and during a fourth step carrying out the aforesaid replacing ofthe pouring tube which has been moved out of alignment with the outletof the supply vessel by a new pouring tube after such time as thereplacement pouring tube has moved into a position beneath the outlet ofthe supply vessel.